CDC events
Hits within 1mm of the best track found (before fitting) are included in the fit.
Blue straws have hits found, green were part of the track-fitting, pink and lime green have a zero-crossing within 40ns of the hit time. The hit for ch 38 looks ok, conclude that fitted track is ok and ch42 & 43 are masked by noise.
What went wrong with ch53? At first glance it looks like the hit signal arrives in sample 119 which is indeed what the tracking software decided. However the fitted track implies that the hit signal should have arrived in sample 110 (similar time to channels 13 and 67). In ch53 the adc value went above the first threshold (161) in sample 113. This threshold was based on pedestal = 61 = the mean adc value in samples 0-99. A local pedestal was then calculated as the spot value approximately 3 samples before from the threshold crossing. This local pedestal was 118 (much higher than normal) and then the threshold crossing was re-found at sample 119. The local pedestal was unusually high because the upward slope of the adc value was unusually small, presumably due to a large noise fluctuation lying beneath the hit signal.
Conclusion: if the local pedestal is very different from the default event pedestal there could be a problem with the hit time.
Ch 10: event pedestal 62, local pedestal 130. Messed up by sudden drop in pedestal before hit arrived.
Ch 56 and 68: assigned hit times look reasonable. Ch 56 has drift-radius 2.5mm from fitted track, ch 68 has drift radius 1.3mm from fitted track.
Ch 10 drift radius is only 0.8mm from fitted track so it should have been included on it. Trackfinding bug, hit time was good.
Ch4: maybe the track split here Ch8: no hit apparent Ch63: hit shape is atypical. First peak was below hit threshold (124) but inflated pedestal for second peak, which was above threshold. Start of event ped=52, localped=103. Hit time was not found because the second peak did not exceed localped+threshold=169.
Ch 33 drift radius is only 1.6mm from fitted track. Hit time appears good but leading edge of the peak is an unusual shape.
Ch 8: Start of event ped=63, localped=98. First exceeded threshold (146) in sample 116 - this would have fitted on the track - but after stepping back to local ped, next threshold localped+5#sigma (165) was not passed until sample 153. First threshold xing is either noise or sitting on top of noise.
Event 16: Largest residual (diff betw drift radius measured and drift radius obtained from fitted track) is 0.4mm Event 19: Largest residual is 0.97mm Event 20: Largest residual is 0.84mm
Return to event 8. These straws have good hit time despite the changing pedestal.
The straws in the track picture are a lighter shade of blue/green if the event and local pedestals differ by > 40 adc units (pedestal sigma is 15-20 adc units).
In the picture below the straws with dotted drift-time circles are those with 5 sigma threshold time - hit time < -0.3 or > 3.3 (outside 3sigma)
Using this to revisit the other events, only 4 track pictures change...
